mmc: sdhci: fix minimum clock rate for v3 controller
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Message ID 3f3b2ac4634802af591a20b1b98dc8d0158aec45.1577962196.git.mirq-linux@rere.qmqm.pl
State Superseded
Headers show
Series
  • mmc: sdhci: fix minimum clock rate for v3 controller
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Commit Message

Michał Mirosław Jan. 2, 2020, 10:51 a.m. UTC
For SDHCIv3+ with programmable clock mode, minimal clock frequency is
still base clock / max(divider). Minimal programmable clock frequency is
always greater than minimal divided clock frequency. Without this patch,
SDHCI uses out-of-spec initial frequency when multiplier is big enough:

mmc1: mmc_rescan_try_freq: trying to init card at 468750 Hz
[for 480 MHz source clock divided by 1024]

Cc: stable@vger.kernel.org
Fixes: c3ed3877625f ("mmc: sdhci: add support for programmable clock mode")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
---
 drivers/mmc/host/sdhci.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

Comments

Adrian Hunter Jan. 14, 2020, 1:08 p.m. UTC | #1
On 2/01/20 12:51 pm, Michał Mirosław wrote:
> For SDHCIv3+ with programmable clock mode, minimal clock frequency is
> still base clock / max(divider). Minimal programmable clock frequency is
> always greater than minimal divided clock frequency. Without this patch,
> SDHCI uses out-of-spec initial frequency when multiplier is big enough:
> 
> mmc1: mmc_rescan_try_freq: trying to init card at 468750 Hz
> [for 480 MHz source clock divided by 1024]

The maximum divisor in programmable clock mode is 1024.  So I do not
understand what is wrong.  Can you explain some more?

> 
> Cc: stable@vger.kernel.org
> Fixes: c3ed3877625f ("mmc: sdhci: add support for programmable clock mode")
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> ---
>  drivers/mmc/host/sdhci.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 275102c0a1bf..0036ddf85674 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -3902,11 +3902,9 @@ int sdhci_setup_host(struct sdhci_host *host)
>  	if (host->ops->get_min_clock)
>  		mmc->f_min = host->ops->get_min_clock(host);
>  	else if (host->version >= SDHCI_SPEC_300) {
> -		if (host->clk_mul) {
> -			mmc->f_min = (host->max_clk * host->clk_mul) / 1024;
> +		if (host->clk_mul)
>  			max_clk = host->max_clk * host->clk_mul;
> -		} else
> -			mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
> +		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
>  	} else
>  		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_200;
>  
>
Michał Mirosław Jan. 14, 2020, 3:53 p.m. UTC | #2
On Tue, Jan 14, 2020 at 03:08:08PM +0200, Adrian Hunter wrote:
> On 2/01/20 12:51 pm, Michał Mirosław wrote:
> > For SDHCIv3+ with programmable clock mode, minimal clock frequency is
> > still base clock / max(divider). Minimal programmable clock frequency is
> > always greater than minimal divided clock frequency. Without this patch,
> > SDHCI uses out-of-spec initial frequency when multiplier is big enough:
> > 
> > mmc1: mmc_rescan_try_freq: trying to init card at 468750 Hz
> > [for 480 MHz source clock divided by 1024]
> 
> The maximum divisor in programmable clock mode is 1024.  So I do not
> understand what is wrong.  Can you explain some more?

This part of code misses the fact, that you can choose (switch) between
base clock mode and programmable clock mode. The code in
sdhci_calc_clk() already does the choosing part. This is actually
required on high programmable clock base to get conformant frequency for
the card initialization phase.

Best Regards,
Michał Mirosław

[...]
> > index 275102c0a1bf..0036ddf85674 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -3902,11 +3902,9 @@ int sdhci_setup_host(struct sdhci_host *host)
> >  	if (host->ops->get_min_clock)
> >  		mmc->f_min = host->ops->get_min_clock(host);
> >  	else if (host->version >= SDHCI_SPEC_300) {
> > -		if (host->clk_mul) {
> > -			mmc->f_min = (host->max_clk * host->clk_mul) / 1024;
> > +		if (host->clk_mul)
> >  			max_clk = host->max_clk * host->clk_mul;
> > -		} else
> > -			mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
> > +		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
> >  	} else
> >  		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_200;
Adrian Hunter Jan. 15, 2020, 7:16 a.m. UTC | #3
On 14/01/20 5:53 pm, Michał Mirosław wrote:
> On Tue, Jan 14, 2020 at 03:08:08PM +0200, Adrian Hunter wrote:
>> On 2/01/20 12:51 pm, Michał Mirosław wrote:
>>> For SDHCIv3+ with programmable clock mode, minimal clock frequency is
>>> still base clock / max(divider). Minimal programmable clock frequency is
>>> always greater than minimal divided clock frequency. Without this patch,
>>> SDHCI uses out-of-spec initial frequency when multiplier is big enough:
>>>
>>> mmc1: mmc_rescan_try_freq: trying to init card at 468750 Hz
>>> [for 480 MHz source clock divided by 1024]
>>
>> The maximum divisor in programmable clock mode is 1024.  So I do not
>> understand what is wrong.  Can you explain some more?
> 
> This part of code misses the fact, that you can choose (switch) between
> base clock mode and programmable clock mode. The code in
> sdhci_calc_clk() already does the choosing part. This is actually
> required on high programmable clock base to get conformant frequency for
> the card initialization phase.

Ok, so please add that explanation to the commit message, and add a comment
in the code too.

> 
> Best Regards,
> Michał Mirosław
> 
> [...]
>>> index 275102c0a1bf..0036ddf85674 100644
>>> --- a/drivers/mmc/host/sdhci.c
>>> +++ b/drivers/mmc/host/sdhci.c
>>> @@ -3902,11 +3902,9 @@ int sdhci_setup_host(struct sdhci_host *host)
>>>  	if (host->ops->get_min_clock)
>>>  		mmc->f_min = host->ops->get_min_clock(host);
>>>  	else if (host->version >= SDHCI_SPEC_300) {
>>> -		if (host->clk_mul) {
>>> -			mmc->f_min = (host->max_clk * host->clk_mul) / 1024;
>>> +		if (host->clk_mul)
>>>  			max_clk = host->max_clk * host->clk_mul;
>>> -		} else
>>> -			mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
>>> +		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
>>>  	} else
>>>  		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_200;

Patch
diff mbox series

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 275102c0a1bf..0036ddf85674 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -3902,11 +3902,9 @@  int sdhci_setup_host(struct sdhci_host *host)
 	if (host->ops->get_min_clock)
 		mmc->f_min = host->ops->get_min_clock(host);
 	else if (host->version >= SDHCI_SPEC_300) {
-		if (host->clk_mul) {
-			mmc->f_min = (host->max_clk * host->clk_mul) / 1024;
+		if (host->clk_mul)
 			max_clk = host->max_clk * host->clk_mul;
-		} else
-			mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
+		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
 	} else
 		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_200;